Plunger tip and sliding method

ABSTRACT

A plunger tip slides along an inner surface of the plunger sleeve and that injects a molten metal into a mold. The plunger tip includes: a tip main body; a ring-shaped hard resin member that is attached to an outer peripheral surface of the tip main body and that is in contact with the inner surface of the plunger sleeve at least during a hot period in which the plunger tip slides along the inner surface of the plunger sleeve; and a silicone resin member positioned between the tip main body and the ring-shaped hard resin member, in which a radial thickness of the silicone resin member during the hot period is thinner than a radial thickness of the silicone resin member during a cold period in which the molten metal is not supplied in the plunger sleeve.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2020-156841 filed on Sep. 18, 2020, incorporated herein by reference in its entirety.

BACKGROUND 1. Technical Field

The present disclosure relates to a plunger tip and a sliding method.

2. Description of Related Art

A plunger tip used in a die casting machine slides in a plunger sleeve. Thus, lubricity and sealing property are required between the plunger tip and an inner surface of the plunger sleeve. In Japanese Unexamined Patent Application Publication No. 2006-035308 (JP 2006-035308 A), a part of an outer peripheral side surface of a tip main body is covered with a hard resin, and the hard resin comes into contact with an inner surface of a plunger sleeve and thus, lubricity and sealing property are provided between the plunger tip and the inner surface of the plunger sleeve.

SUMMARY

Although the hard resin used for the plunger tip is required to have heat resistance, a hard resin having high heat resistance has a large coefficient of thermal expansion in general. Thus, in JP 2006-035308 A, when it is designed such that the hard resin is in contact with the inner surface of the plunger sleeve in a state in which the molten metal is supplied in the plunger sleeve (in the present disclosure, referred to as “during a cold period” or a “cold period”), the diameter of the hard resin is increased due to thermal expansion when the plunger tip slides in the plunger sleeve to inject the molten metal supplied in the plunger sleeve 200 into the mold (in the present disclosure, referred to as “during a hot period” or a “hot period”). Thus, the frictional resistance during sliding becomes too large. In contrast, if the size of the diameter of the hard resin is designed in consideration of the thermal expansion of the hard resin during the hot period so that the frictional resistance during sliding does not become too large, there is a possibility that the sealing property of the hard resin and the inner surface of the plunger sleeve during the hot period cannot be sufficiently obtained when the thermal expansion of the hard resin is not as designed, and the like.

The present disclosure has been made to solve such a problem, and the object of the present disclosure is to provide a plunger tip and a sliding method that can further reduce a frictional resistance during sliding while ensuring a sealing property during the hot period.

A plunger tip slides along an inner surface of the plunger sleeve and that injects a molten metal into a mold. The plunger tip includes: a tip main body; a ring-shaped hard resin member that is attached to an outer peripheral surface of the tip main body and that is in contact with the inner surface of the plunger sleeve at least during a hot period in which the plunger tip slides along the inner surface of the plunger sleeve; and a ring-shaped elastic member positioned between the tip main body and the ring-shaped hard resin member, in which a radial thickness of the ring-shaped elastic member during the hot period is thinner than a radial thickness of the ring-shaped elastic member during a cold period in which the molten metal is not supplied in the plunger sleeve.

In a sliding method according to the present disclosure, a plunger tip slides along an inner surface of a plunger sleeve and injects a molten metal into a mold. The plunger tip includes: a tip main body; a ring-shaped hard resin member that is attached to an outer peripheral surface of the tip main body and that is in contact with the inner surface of the plunger sleeve at least during a hot period in which the plunger tip slides along the inner surface of the plunger sleeve; and a ring-shaped elastic member positioned between the tip main body and the silicone resin member, in which a radial thickness of the ring-shaped elastic member during the hot period is thinner than a radial thickness of the ring-shaped elastic member during a cold period in which the molten metal is not supplied in the plunger sleeve.

In the plunger tip according to the present disclosure, since the ring-shaped elastic member becomes thinner during the hot period than during the cold period, even when the diameter of the ring-shaped hard resin member is increased due to thermal expansion, it is possible to suppress the frictional resistance between the inner surface of the plunger sleeve and the ring-shaped hard resin member from being increased. Further, since the ring-shaped hard resin member comes into contact with the inner surface of the plunger sleeve at least during the hot period, it is possible to secure the sealing property during the hot period. This makes it possible to provide the plunger tip that can further reduce the frictional resistance during sliding while ensuring the sealing property during the hot period.

In the sliding method according to the present disclosure, since the ring-shaped elastic member becomes thinner during the hot period than during the cold period, even when the diameter of the ring-shaped hard resin member is increased due to thermal expansion, it is possible to suppress the frictional resistance between the inner surface of the plunger sleeve and the ring-shaped hard resin member from being increased. Further, since the ring-shaped hard resin member comes into contact with the inner surface of the plunger sleeve at least during the hot period, it is possible to secure the sealing property during the hot period. This makes it possible to provide the sliding method that can further reduce the frictional resistance during sliding while ensuring the sealing property during the hot period.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like signs denote like elements, and wherein:

FIG. 1 is a partial cross-sectional view showing a plunger tip and a plunger sleeve according to a first embodiment of the present disclosure; and

FIG. 2 is a partial cross-sectional view showing a plunger tip and a plunger sleeve according to a second embodiment of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS First Embodiment

Hereinafter, a first embodiment of the present disclosure will be described with reference to the drawings. However, the disclosure is not limited to the following first embodiment. The following description and drawings are simplified as appropriate for the sake of clarity.

FIG. 1 is a partial cross-sectional view showing a plunger tip 100 and a plunger sleeve 200 according to the first embodiment of the present disclosure. On the left side of FIG. 1, the plunger tip 100 and the plunger sleeve 200 in a state in which a molten metal is not supplied in the plunger sleeve 200 (hereinafter, referred to as “during a cold period” or “a cold period” in the present specification) is shown. On the right side of FIG. 1, the plunger tip 100 and the plunger sleeve 200 in a state in which the molten metal is supplied in the plunger sleeve 200 (hereinafter, referred to as “during a hot period” or “a hot period” in the present specification) is shown. The plunger tip 100 slides along an inner surface of the plunger sleeve 200 having a cylindrical shape, and injects the molten metal supplied in the plunger sleeve 200 into a mold. As shown in FIG. 1, the plunger tip 100 includes a tip main body 101, a ring-shaped hard resin member 102 (hereinafter, simply referred to as a “hard resin member 102”), and a ring-shaped silicone resin member 103 (hereinafter, simply referred to as a “resin member 103”) serving as a ring-shaped elastic member.

The tip main body 101 has a cylindrical shape, and a cooling device can be provided inside the cylindrical shape. Here, the cooling device is, for example, a cooling pipe or the like that serves as a flow path for a refrigerant. When the cooling device is not required, the tip main body 101 may have a columnar shape instead of a cylindrical shape. The tip main body 101 is made of heat-resistant tool steel or the like. Further, the tip main body 101 may be formed of a copper alloy such as beryllium copper.

Further, in at least a part of the outer peripheral surface, the tip main body 101 has a groove portion 101A extending along a circumferential direction in which the hard resin member 102 and the silicone resin member 103 can be disposed. The depth of the groove portion 101A is determined by the thickness of the hard resin member 102 and the thickness of the silicone resin member 103 disposed in the groove portion 101A. Specifically, the silicone resin member 103 and the hard resin member 102 are disposed in this order in the groove portion 101A toward an outer radial side of the tip main body 101. The groove portion 101A has a depth in which the hard resin member 102 can come into contact with the inner surface of the plunger sleeve 200, at least during the hot period. As a result, the sealing property between the inner surface of the plunger sleeve 200 and the hard resin member 102 during the hot period can be ensured. Further, the depth of the groove portion 101A may be a depth in which the hard resin member 102 comes into contact with the inner surface of the plunger sleeve 200 during the cold period. As a result, the sealing property between the inner surface of the plunger sleeve 200 and the hard resin member 102 during the cold period can be more surely ensured. Specifically, the sealing property can be ensured until the thermal expansion of the hard resin member 102 is completed (in the initial stage of the hot period). Here, “the thermal expansion of the hard resin member 102 is completed” means that the temperature of the hard resin member 102 and the ambient temperature become substantially constant, and the amount of thermal expansion of the hard resin member 102 becomes substantially constant.

Further, the diameter of a part of the tip main body 101 excluding the groove portion 101A is slightly smaller than the inner diameter of the plunger sleeve 200. In casting using a die casting machine, the plunger tip 100 and the plunger sleeve 200 are thermally expanded by the heat of the molten metal or the like. Therefore, the diameter of the tip main body 101 is formed to be slightly smaller than the inner diameter of the plunger sleeve 200 so that the thermal expansion of the tip main body 101 during the hot period can be allowed. In other words, the diameter of the tip main body 101 is such that a minute gap is formed between the outer surface of the tip main body 101 and the inner surface of the plunger sleeve 200 in a state in which the plunger sleeve 200 and the tip main body 101 are thermally expanded. This makes it possible to prevent frictional resistance from being generated between the inner surface of the plunger sleeve 200 and the outer surface of the plunger tip 100 when sliding the plunger tip 100 inside the plunger sleeve 200.

The hard resin member 102 is a ring-shaped member formed of a hard resin having a high heat resistance. Further, the hard resin member 102 is attached to the inside of the groove portion 101A of the tip main body 101 and on the outer radial side of the tip main body 101 of the silicone resin member 103 attached to the groove portion 101A.

Further, the hard resin member 102 has a radial thickness that allows contact with the inner surface of the plunger sleeve 200 at least during the hot period in which the plunger tip 100 slides along the inner surface of the plunger sleeve 200.

Specifically, during the cold period, that is, in the state in which the silicone resin member 103 described below is not compressed, the hard resin member 102 may have a radial thickness so as to provide a slight gap between the inner surface of the plunger sleeve 200 and the hard resin member 102. The slight gap has a size in which the amount of thermal expansion of the hard resin member 102 during the hot period and the amount of compression of the silicone resin member 103 described later is taken into consideration. More specifically, the slight gap has a size in which it is possible to prevent the inner surface of the plunger sleeve 200 and the hard resin member 102 from coming into contact and prevent an excessive frictional resistance from being generated when the plunger tip 100 slides along the inner surface of the plunger sleeve 200, due to the hard resin member 102 being thermally expanded by the heat of the molten metal during the hot period and the silicone resin member 103 being compressed by the thermal expansion of the hard resin member 102. As a result, the sealing property during the hot period is ensured, and the frictional resistance between the inner surface of the plunger sleeve 200 and the hard resin member 102 when sliding the plunger tip 100 can be prevented from becoming excessively large.

Alternatively, during the cold period, in the state in which the silicone resin member 103 described below is not compressed, the hard resin member 102 may have a radial thickness in which the inner surface of the plunger sleeve 200 and the hard resin member 102 come into contact. In this case, it is possible to prevent an excessive frictional resistance from being generated between the inner surface of the plunger sleeve 200 and the hard resin member 102, due to the hard resin member 102 being thermally expanded and the silicone resin member 103 being compressed by the thermal expansion of the hard resin member 102, during the hot period. Further, since the inner surface of the plunger sleeve 200 and the hard resin member 102 are in contact during the cold period, the sealing property can be ensured until the thermal expansion of the hard resin member 102 is completed (the initial stage of the hot period).

The silicone resin member 103 is a ring-shaped member formed of a heat-resistant silicone resin. Further, the silicone resin member 103 is attached to the inside of the groove portion 101A of the tip main body 101 and on the inner radial side of the tip main body 101 of the hard resin member 102 attached to the groove portion 101A. That is, the silicone resin member 103 is positioned between the tip main body 101 and the hard resin member 102. Further, the silicone resin member 103 has, for example, a static shear modulus of 0.2 MPa or more and 1.0 MPa or less. Then, although the silicone resin member 103 slightly thermally expands during the hot period, the silicone resin member 103 is actually compressed by being pushed by the thermally expanded hard resin member 102. In other words, the radial thickness of the silicone resin member 103 during the hot period is thinner than the radial thickness of the silicone resin member 103 during the cold period. Further, during the cold period, the silicone resin member 103 is not substantially compressed.

Next, a sliding method according to the first embodiment in which a plunger tip 100 is slid along the inner surface of the plunger sleeve 200 to inject a molten metal into a mold will be described.

First, as shown on the left side of FIG. 1, the silicone resin member 103 is not compressed during the cold period, and the hard resin member 102 is in contact with the inner surface of the plunger sleeve 200.

Next, as shown on the right side of FIG. 1, the molten metal is supplied in the plunger sleeve 200, the molten metal causes the plunger tip 100 and the plunger sleeve 200 to thermally expand slightly and the hard resin member 102 to be thermally expanded significantly, and the silicone resin member 103 is compressed by the thermally expanded hard resin member 102. That is, the radial thickness of the silicone resin member 103 during the hot period is thinner than the radial thickness of the silicone resin member 103 during the cold period.

Then, the plunger tip 100 is slid along the inner surface of the plunger sleeve 200 to inject the molten metal supplied in the plunger sleeve 200 into the mold. At this time, while the hard resin member 102 is thermally expanded, the silicone resin member 103 is compressed by the amount of thermal expansion of the hard resin member 102. Thus, the frictional resistance during sliding does not become excessively large. Further, since the inner surface of the plunger sleeve 200 and the hard resin member 102 are already in contact during the cold period, the sealing property can be ensured until the thermal expansion of the hard resin member 102 is completed (the initial stage of the hot period).

In the plunger tip 100 and the sliding method according to the first embodiment described above, since the silicone resin member 103 becomes thinner during the hot period than during the cold period, even when the diameter of the hard resin member 102 is increased due to thermal expansion, it is possible to suppress the frictional resistance between the inner surface of the plunger sleeve 200 and the hard resin member 102 during sliding of the plunger tip 100 from being increased. Further, since the hard resin member 102 comes into contact with the inner surface of the plunger sleeve 200 at least during the hot period, it is possible to secure the sealing property during the hot period. This makes it possible to provide the plunger tip 100 and the sliding method that can further reduce the frictional resistance during sliding while ensuring the sealing property during the hot period.

Second Embodiment

Next, a plunger tip 100A according to a second embodiment of the present disclosure will be described with reference to FIG. 2. The following description and drawings are simplified as appropriate for the sake of clarity.

As shown in FIG. 2, the plunger tip 100A according to the second embodiment is different from the plunger tip 100 according to the first embodiment in that an elastic spring 104 is provided instead of the silicone resin member 103 as the ring-shaped elastic member. Thus, in the plunger tip 100A according to the second embodiment, the same components as those of the plunger tip 100 according to the first embodiment are indicated with the same reference numerals, and the description thereof will be omitted.

The elastic spring 104 is a ring-shaped leaf spring, and the cross-sectional shape of the ring in the radial direction is substantially U-shaped. Further, the elastic spring 104 is attached to the inside of the groove portion 101A of the tip main body 101 and on the inner radial side of the tip main body 101 of the hard resin member 102 attached to the groove portion 101A. That is, the elastic spring 104 is positioned between the tip main body 101 and the hard resin member 102. Further, during the hot period, the elastic spring 104 contracts by being pushed by the thermally expanded hard resin member 102. In other words, the radial thickness of the elastic spring 104 during the hot period is thinner than the radial thickness of the elastic spring 104 during the cold period. Also, during the cold period, the elastic spring 104 is not substantially compressed.

Next, a sliding method according to the second embodiment in which the plunger tip 100 is slid along the inner surface of the plunger sleeve 200 to inject the molten metal into the mold will be described.

First, as shown on the left side of FIG. 2, the elastic spring 104 is not compressed during the cold period, and the hard resin member 102 is in contact with the inner surface of the plunger sleeve 200.

Next, as shown on the right side of FIG. 2, the molten metal is supplied in the plunger sleeve 200, the molten metal causes the plunger tip 100 and the plunger sleeve 200 to thermally expand slightly and the hard resin member 102 to be thermally expanded significantly, and the elastic spring 104 pressed by the thermally expanded hard resin member 102 is shrunk. That is, the radial thickness of the elastic spring 104 during the hot period is thinner than the radial thickness of the elastic spring 104 during the cold period.

Then, the plunger tip 100 is slid along the inner surface of the plunger sleeve 200 to inject the molten metal supplied in the plunger sleeve 200 into the mold. At this time, while the hard resin member 102 is thermally expanded, the elastic spring is shrunk by the amount of thermal expansion of the hard resin member 102. Thus, the frictional resistance during sliding does not become excessively large. Further, since the inner surface of the plunger sleeve 200 and the hard resin member 102 are already in contact during the cold period, the sealing property can be ensured until the thermal expansion of the hard resin member 102 is completed (the initial stage of the hot period).

In the plunger tip 100 and the sliding method according to the second embodiment described above, since the elastic spring 104 becomes thinner during the hot period than during the cold period, even when the diameter of the hard resin member 102 is increased due to thermal expansion, it is possible to suppress the frictional resistance between the inner surface of the plunger sleeve 200 and the hard resin member 102 during sliding of the plunger tip 100 from being increased. Further, since the hard resin member 102 comes into contact with the inner surface of the plunger sleeve 200 at least during the hot period, it is possible to secure the sealing property during the hot period. This makes it possible to provide the plunger tip 100A and the sliding method that can further reduce the frictional resistance during sliding while ensuring the sealing property during the hot period.

The present disclosure is not limited to the above embodiments, and can be appropriately modified without departing from the spirit thereof. 

What is claimed is:
 1. A plunger tip that slides along an inner surface of a plunger sleeve and that injects a molten metal into a mold, the plunger tip comprising: a tip main body; a ring-shaped hard resin member that is attached to an outer peripheral surface of the tip main body and that is in contact with the inner surface of the plunger sleeve at least during a hot period in which the plunger tip slides along the inner surface of the plunger sleeve; and a ring-shaped elastic member positioned between the tip main body and the ring-shaped hard resin member, wherein a radial thickness of the ring-shaped elastic member during the hot period is thinner than a radial thickness of the ring-shaped elastic member during a cold period in which the molten metal is not supplied in the plunger sleeve.
 2. The plunger tip according to claim 1, wherein the ring-shaped elastic member is formed of a silicone resin.
 3. The plunger tip according to claim 1, wherein the ring-shaped elastic member is an elastic spring.
 4. The plunger tip according to claim 1, wherein the ring-shaped hard resin member is in contact with the inner surface of the plunger sleeve both during the hot period and during the cold period.
 5. A sliding method in which a plunger tip is slid along an inner surface of a plunger sleeve to inject molten metal into a mold, the plunger tip comprising: a tip main body; a ring-shaped hard resin member that is attached to an outer peripheral surface of the tip main body and that is in contact with the inner surface of the plunger sleeve at least during a hot period in which the plunger tip slides along the inner surface of the plunger sleeve; and a ring-shaped elastic member positioned between the tip main body and the ring-shaped hard resin member, wherein a radial thickness of the ring-shaped elastic member during the hot period is thinner than a radial thickness of the ring-shaped elastic member during a cold period in which the molten metal is not supplied in the plunger sleeve.
 6. The sliding method according to claim 5, wherein the ring-shaped elastic member is formed of a silicone resin.
 7. The sliding method according to claim 5, wherein the ring-shaped elastic member is an elastic spring.
 8. The sliding method according to claim 5, wherein the ring-shaped hard resin member is in contact with the inner surface of the plunger sleeve both during the hot period and during the cold period. 